Wafer fabrication is the process by which integrated circuits (ICs) are manufactured. It is basically a process by which a silicon wafer substrate is repeatedly coated, etched and rinsed to form ICs. The wafer is then cut to separate the ICs, which may then be molded into packages for mounting on circuit boards or the like.
Wafer fabrication is a multivariate process and subject to manufacturing defects, however slight they may be. A highly competitive wafer fabrication industry pays a great deal of attention to the occurrence and impact of these defects, the most extreme of which can lead to a wafer batch being scrapped entirely. Accordingly, the industry has developed a multitude of WATs that narrowly identify sub-optimal wafer fabrication. Initially, WATs were used to allow manufacturers to determine whether or not to accept a lot of completed wafers into inventory as sellable products. Over time, WATs began to be used to allow manufacturers to direct their wafer manufacturing and inventory more precisely.
The wafer fabrication industry is largely demand-driven. Consequently, wafer fabrication tends to be carried out with specific end products in mind. As such, a premium is placed on an understanding of precisely how a certain batch or lot of wafers will perform.